This Phase II/III, randomized, comparative, double-blind multicenter trial is designed to determine the comparative effectiveness of 3TC+ZDV versus the better of ddI monotherapy versus ZDV+ddI combination therapy with respect to HIV disease progression. The safety and tolerance of 3TC/ZDV in ZDV naive, symptomatic children will be evaluated. The study will also further validate the correlation between quantitative plasma RNA levels and HIV disease progression in children. There have been 528 patients accrued nationwide out of a target of 740. The ZDV+ddI arm is closed to accrual, but the blinded treatment arm was continued on subjects already enrolled. A secondary study objective to compart ZDV+ddI vs the other two arms with respect to changes in RNA was added.